Sector radio beacon

ABSTRACT

To provide a rotating radiation pattern in a given sector, an antenna which radiates a carrier frequency F is flanked, substantially along a line, on one side by a directional antenna which radiates a frequency F- 15 Hz. and on the other side by a directional antenna radiating a frequency F+15 Hz. and a directional antenna radiating a frequency F+135 Hz. The directional antennas radiate in a direction substantially perpendicular to said line. The antenna spacing is dependent upon the carrier frequency and the desired width of said sector.

OR EeSBY vU Q U nlwu Dlflltib r atclu.

Ernst Kramar Ptorzhclm, Germany Mar. 4, 1969 June 22, 1971 InternationalStandard Electric Corporation New York, N.Y.

Inventor Appl. No. Filed Patented Assignee SECTOR RADIO BEACON 4 Claims,5 Drawing Figs:

U.S.Cl

Int. Cl Field of Search References Cited UNITED STATES PATENTS l/ 1951Luck F-75Hz F F 75Hz 2,978,701 4/1961 Pickles 3.305.866 2/1967 EarpPrimary Examiner-Richard A. Farley Assistant Examiner-Richard E. BergerAttorneys-C. Cornell Remsen, .lr., Walter J. Baum, Percy P.

Lantzy, Philip M. Bolton, Isidore Tqgut and Charles L. Johnson, Jr.

PATENTEBJUNZZIHH 3,587,099

Fig. 3 Fig.4

INVENTOR ERNST KRAMAR Maw 4% ATTORNEY ssc'ronnxmo BEACON BACKGROUND OFTHE INVENTION 1. Field of the Invention The present invention relates toa beacon, and in particular to onewhich provides a rotating pattern in apredetermined sector.

2. Description of Prior Art Many interesting instrument landing systemshave been proposed, however, their implementation requires .eithermodification or addition of equipment on board aircrafts.

However, airborne T acan receivers presently being used for .en routenavigation may be used without modification for landing guidanceprovided that a Tacan type signal is made present in a sector whichincludes the runway approach.

. Directional beacons which provide rotating Tacan signals are wellknown. However, these beacons are not effective if one simply desiresrotating radiation patterns to be present in a sectorfGenerally these.conventional beacons use physically rotating parasitics to produce the.rotating field and are relatively cumbersome and difficult to transport.

SUMMARY OF THE INVENTION radiating a secondfrequency located at adistance from said first means, which distance is determined by saidfirst carrier frequency and the desired width of said sector, and'thirdmeans for radiating a third frequency located at asecond distance fromsaid first means.

BRIEF DESCRIPTION OFTHE DRAWINGS The above-mentioned and other objectsof the invention will become apparent by reference to the followingdescription in conjunction with the I accompanying drawings, in which: I

FIG. 1 illustrates a radiation pattern resulting from the applicationofin-phase signals to spaced dipoles.

FIG. 2 illustrates a radiation pattern resulting from the application ofantiphase signals to spaced dipoles.

FIG. 3 illustrates a radiation pattern in a sector resulting from. theapplication of different frequencies to spaced dipoles.

FIG. 4 illustrates an in-line arrangement of spacedantennas according tothe invention.

FIG. 5 illustrates a second in-line arrangement of spaced antennasaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS To explain the mode ofoperation of the invention, it is assumed that two dipoles spaced, forexample, one wavelengthapart, radiate the same frequency. A four-loberadiation pattern is thus obtained having an approximately 60 apertureangle. By shifting in-phase one or both feed voltages, with respect toeach other, the entire pattern may be arbitrarily placed. FIG. I andFIG. 2 show respectively the patterns produced by feeding the dipoleswith in-phase and out-ofphase voltages. If, for example, thetphase ofthe feed voltage for dipole 2 is continuously shiftedywitli respect tothe feed voltage coupled to dipole I, Ethe -radiatioh lobes rotateclockwise; if the frequency of dipole 2 is, for example, Hz.

higher than the frequency fed to dipole l, the entire radiation patternrotates clockwise l5times per second.

Within a sector of 60, assuming :for example purposes, which is formedby both zeros of the pattern perpendicular to the dipole plane in theapproach direction, 360 electrical degrees are passed within 60 ofazimuth so that 1 of azimuth corresponds to 6 electrical degrees.

However, in order to make the scale reading easier, the width of thesector could have been chosen such that, for example, 1 of azimuthcorresponds to 1.0 electrical degrees of an airborne indicator. Thiswould require a i 18 sector width. The dipole spacing required toachieve the above is d 5111') -A= 1.6 A.

In order to make the above-described approach beacon compatible withTacan receivers, it should be considered that the modulation sidebandsof 15 Hz. and Hz. produced by a Tacan ground beacon are each radiatedwith a modulation index of 18 percent. The current ratio between thedipole 1 radiating the frequency F and the dipole 2 as illustrated inFIG. 3 radiating the frequency F+f, where f=l5 Hz. must be selected in aratio 110.18. Reference pulse trains may be transmitted by the dipolefed withthe frequency F as in the standard Tacan system so that a phasecomparison can be made as is usual in the receiver.

The single sideband radiation above-described can be converted to doublesideband modulation by the addition of another dipole 3 as illustratedin FIG. 4 and fed with energy of a frequency F- where f is, for example,15 Hz. The resulting radiation field has the characteristics of pureamplitude modulation. This is particularly useful because of a resultingreduction of nonlinear distortion.

The accuracy of the above-described embodiment is sufficiently accuratefor establishing a clearance pattern. To improve the accuracy, however,a nine-lobe pattern is superimposed on the single lobe pattern withinthe sector. This is achieved, for example, by placing another dipole 4,as shown in FIG. 4, at a distance of 9 '(5/1r) A from the dipole 1, saiddipole 4 being fed with a frequency F+9f(F+l35 Hz.). With the sameamplitude ratio of 1:0.18 of the If energy with respect to the dipole 1(main antenna) nine radiation maxima and minimal in total are obtainedwithin the sector of i 18.3 1 which rotate at a speed of I35 Hz. Thereference signals required for fine phase measurement transmitted in thesame manner as the reference signals for coarse phase measurement towit, as a modulation of the carrier wave. Thus, the amplitude modulationresulting from the antenna arrangement and the particular feeding ofsaid antenna, detected in the airborne receiver within said sector of36, corresponds to the radiation of a conventional Tacan transmittingsystem.

At a dipole spacing of 15 A, the antenna arrangement constitutes awide-base system and offers well known advantages with respect tomultipath propagational effects of the rf signals, the system therefore,operates more favorably than an omnidirectional Tacan antenna.

It is suitable to concentrate radiation, for example, with the aid ofhorn radiators, as shown in FIG. 4, having a radiation pattern ofapproximately 45 at the half-power points. This prevents a lateral andbackward radiation of rf energy and considerably reduces the ambiguityof the measurement at the receiving end.

In order to ensure that the antenna system radiates mainly in thedesired forward direction and that the energy radiated in thebackwarddirectionis as low as possible, the main antenna (1, FIG. 4) isoffset forward by one-eighth wavelength. This means can however be usedsuccessfully only, if a double sideband system is used, i.e. if also theantenna 3, FIG. 4 exists and is fed by lower sideband energy (F-IS cls).

If the transmitter feeding dipole l is designed as a transponder, thereceiver of which picks up distance interrogation signals from aircraftby which the transmitter is modulated, in a way known per se, theaircraft may determine its distance from the beacon. If, however,interrogation signals arenot received, the carrier wave may be modulatedby random pulses.

In practice it has been found that it is often important to know atleast the distance at any azimuth angle also outward said predeterminedsector when approaching said radio beacon, or when flying round theradio beacon during a waiting period, particularly after an unsuccessfullanding attempt.

It is, therefore, another important feature of the invention that themain antenna is an omnidirectional antenna, whilst the sideband antennaeare unidirectional antennae (F IG. 5

Assuming that for the main transmitter (dipole l) a pulse peak energy ofapproximately 1 kw. is required, it is sufficient to have approximately40 w. pulse peak energy for the sideband transmitters.

It will be noted that the output of the transmitter feeding the mainantenna 1 must be somewhat greater in the case of an omnidirectionalantenna than for a unidirectional antenna. lt will be selected in knownmanner such that the desired degree of modulation is achieved inconjunction with the sideband energy for azimuth determination.

Between the main transmitter and the sideband transmitters, a fixedphase relationship must exist with respect to the difference frequenciesas well as in respect to the pulse trains. The generation of separatecarrier and sideband frequencies having such proper phase relationshipis well known.

1 claim:

1. A beacon for providing a rotating radiation field in a predeterminedsector, comprising:

an omnidirectional antenna for radiating a first carrier frequency;

a first directional antenna located at a first distance from saidomnidirectional antenna, which distance is determined by said firstcarrier frequency and the desired width of said sector, said firstdirectional antenna radiating a second frequency higher than saidcarrier frequency by a predetermined difference; and

a second directional antenna for radiating a third frequency located ata second distance from said omnidirectional antenna, said seconddistance equal to an integral multiple of said first distance, saidthird frequency being higher than said carrier frequency by an integralmultiple of said predetermined difference, and said first and seconddirectional antennas arranged substantially in a line with saidomnidirectional antenna.

2. A beacon, according to claim 1, further including means for radiatinga fourth frequency located at a distance from said omnidirectionalantennas which is a multiple, including one, of said first distance. 3

3. A beacon, according to claim 2, wherein said second and fourthfrequencies are higher and lower respectively than said carrierfrequency by a predetermined frequency difference.

4. A beacon, according to claim 2, wherein said means includes a thirddirectional antenna.

1. A beacon for providing a rotating radiation field in a predeterminedsector, comprising: an omnidirectional antenna for radiating a firstcarrier frequency; a first directional antenna located at a firstdistance from said omnidirectional antenna, which distance is determinedby said first carrier frequency and the desired width of said sector,said first directional antenna radiating a second frequency higher thansaid carrier frequency by a predetermined difference; and a seconddirectional antenna for radiating a third frequency located at a seconddistance from said omnidirectional antenna, said second distance equalto an integral multiple of said first distance, said third frequencybeing higher than said carrier frequency by an integral multiple of saidpredetermined difference, and said first and second directional antennasarranged substantially in a line with said omnidirectional antenna.
 2. Abeacon, according to claim 1, further including means for radiating afourth frequency located at a distance from said omnidirectionalantennas which is a multiple, including one, of said first distance. 3.A beacon, according to claim 2, wherein said second and fourthfrequencies are higher and lower respectively than said carrierfrequency by a predetermined frequency difference.
 4. A beacon,according to claim 2, wherein said means includes a third directionalantenna.